1. Field of the Invention
The present invention relates to a vehicle body frame for a motorcycle and a fabrication method for manufacturing the same.
2. Description of Background Art
With reference to FIG. 7, a perspective view is illustrated of a representative vehicle body frame for a motorcycle. The frame 100 for a motorcycle is integrated by welding and includes a head pipe 101, upper longitudinal pipes 102, lower longitudinal pipes 103 (one of the pipes 103 is not illustrated), pivot plates 104 and a cross pipe 105.
FIG. 8 is a conventional flow diagram for fabricating a vehicle body frame and the designation STXXX is utilized to designate a particular step number.
ST111: The head pipe is fabricated by a gravity die casting process. The gravity die casting process is also simply referred to as a die casting process and is a fabrication method in which a metal mold is used in place of a sand mold, molten aluminum is injected into the metal mold and a feeding head is applied thereon. Only gravity is utilized on the molten metal and a metal mold is used. Accordingly, the process is also referred to as xe2x80x9cgravity die casting.xe2x80x9d Since the molten metal comprises aluminum, for several tens of thousands of times it is feasible for supplying the molten metal injection into a metal mold made of gray cast iron (FC) or structural carbon steel. The cost of the mold can be reduced as compared with a sand mold.
The gravity die casting is preferably adopted for parts of a motorcycle having more or less complicated shapes because gases are not entrapped and the casting surface is excellent since the injection speed is slow.
ST112: By projecting shot grains onto or buffing a provided head pipe cast article, the surface is finished.
ST113: Similar to ST111, the pivot plates are fabricated by the gravity die casting process.
ST114: By projecting shot grains onto or buffing provided pivot plates cast articles, the surfaces are finished.
ST115: Upper/lower longitudinal pipes as well as the cross pipe are fabricated by drawing or extrusion. Pipes or bars having uniform sections can be fabricated by drawing or extrusion swiftly and in mass production.
ST116: The upper/lower longitudinal pipes and the cross pipe are suitably cut and subjected to bending.
ST117: The above-described head pipes, upper/lower longitudinal pipes, pivot plates and cross pipe are integrated by welding.
ST118: The product is subjected to alumite treatment and an anodic oxidation coating is formed on the surface. Thereby, a beautiful vehicle body frame can be fabricated.
However, according to the gravity die casting, as mentioned above, the injection speed is slow and accordingly, the productivity is low which hinders a reduction in fabrication cost of the vehicle body frame.
Hence, it is an object of the present invention to achieve a reduction in fabrication cost of the vehicle body frame by improving the constitution and the fabrication method.
According to the present invention, a vehicle body frame for a motorcycle is constituted of integrating pipes made of aluminum and a plurality of aluminum cast parts by welding. The portions or the total of the plurality of aluminum cast parts are die cast products.
A die cast product is excellent in the production efficiency, resulting in achieving low cost of a cast product. Hence, by making the die cast products portions of constituent parts, the fabrication cost of a vehicle body frame is reduced.
According to the present invention, a vehicle body frame for a motorcycle is fabricated by the steps of integrating aluminum series die cast products and aluminum series non-die cast products fabricated by a method other than die casting, subjecting an integrated article to an alumite treating and coating only die cast portions.
A state of the skin is deteriorated in a die cast product in comparison with a non-die cast product. Therefore, when alumite treating is completed, a die cast portion of an alumite coating does not have as good an appearance as compared with other portion thereof. Hence, the appearance of the vehicle body frame is maintained by coating only the die cast portion.
Further scope of applicability of the present invention will become apparent from the detailed description given hereinafter. However, it should be understood that the detailed description and specific examples, while indicating preferred embodiments of the invention, are given by way of illustration only, since various changes and modifications within the spirit and scope of the invention will become apparent to those skilled in the art from this detailed description.